Copper plating



Patented Dec. '6, 1932 UNITED STATES- PATENT OFFICE WILLI M PEAoocx, JR,or PHILADELPHIA, PENNSYLVANIA, Ass'IeNon, '10 PEACOGK LABORATORIES, nm,or PHILADELPHIA, PEN IsYLvANLA, A CORPORATION or PENN- SYLVAJN'IA NoDrawing.

This invention relates generally to the manufacture of glass mirrors andmore particularly to an improved method of or process for applying aprotective coating or backing of metal over the rear surface of thereflecting medium, t he latter being ordinarily applied to the glass inthe form of a closely adhering thin film or layer of silver, gold orother such metal having the usualr ecting qualities.

Upon investigating the problem of mirror deterioration, it has beenfound that among the primary causes of such deterioration is thepresence of water vapor in the atmosl 5 phere with its attendantfrequent condensation upon the mirror, the presence of salt in themoisture which comes into contact with the mirror, and the ever presenthydrogen sulphide in the atmosphere, this latter being noticeablyconcentrated near cities and being evidenced by the rapid tarnishing ofsilver in homes. It is well known also that the useful life of a mirroris considerably reduced when subjected to intense heat.

In orderto protect the reflecting films of mirrors and the like from thedeleterious A efi'ects of an extremely acid or alkaline atmosphere aswell as from moisture or heat, various attemptshave been made from timeto time and prior to this invention to apply to the reflecting film ofthe mirror metallic coatings or backings having the property of sealingthe reflecting filmor medium from the destructive influence ofatmosphere and excessive temperature. Not only has it been proposed toemploy different kinds of protective coatings or backings but variousmethods have been employed to apply the same to the film which it wasdesired to protect. One of the more common methods has been toelectrolytically'deposit a coating of metallic copper. directly on themetallic re fleeting film, such as silver. Inasmuch as this silver filmis ordinarily extremely thin it has been found that the copper electro-COPPER PLATING Application filed November 21 1930. Serial No. 497,837.

lytically deposited thereon eventually combined with the silver to forma blue streak thereby spoiling the mirror for its intended This reactionbetween the silver purpose. film and its electrolytically depositedcoating of copper is primarily due to the relative.

position of these metals in the electro-chemical scale, thecharacteristic blue streak being particularly noticeable when the mirroris subjected to the influence of the atmosphere which latter acts moreor less in the nature; of'an electrolyte.

It is among the objects of the-present invention to. provide a new andimproved method of applying to the-reflecting -film of a glass mirror aprotective backing or coating of metal for effectively sealing therefleeting film from the deleterious effects of atmosphere, moisture andexcessive tempera-- tures.

A further object if the invention is to provide a method for applying ametallic coating or backing to a mirror wherein the possibility for thebacking to react with the reflecting film is effectually precluded.

Still another object of the invention is the provision of a new andimproved method for applying a protective coating of metal by a processother than electrolytic-deposition and which involves merely a brushing,spraying or simllar operation and wherein the use of expensive equipmentand skilled labor is en tirelyeliminated.

A'stillfurther object of the invention i stoprovide a new and improvedmethod or process for preparing the protective metal for application tothe mirror, the metal so prepared being of powdered form and eachgranule thereof having a more or less leafyphysical structureso thatwhen the powdered metal is applied to the mirror the granules Ehereoflay shingle-like over the reflecting A still further object of theinvention'is the provision of a mixture consisting of fine- #y groundmetal and a conveyor or vehicle r maintaining the metal in suspension,the mixture being ada ted to be inexpensively and readily applie as aprotective coating for mirrors with the vehicle or conveyor thereofserving effectually as a binder for the ground metal at the same timethat it prevents actual metallic contact between themetallicreflectingsfilm and its metallic protective coating. lectrolytic actionbetween said film and coating in the presence of atmosphere having acidor alkaline characteristics is thus effectively precluded.

Other objects and advantages of this inventlon will appear morefullyhereinafter.

While in the following description of the present invention particularreference is had er as the protective coating ure metallic copperprepared as described immediately hereinafter is added to 24 ozs. of theshellac solution. This pure metallic copper is prepared by grinding andpowdering the same,'ethylene glycol being employed as the lubricationand flotation medium in the grinding of'themetal. It is prefper Whl.erable to use ethylene glycol for this purpose because it reduces thepossibility of adulteratmgthe ground metal with any organic impur ties.Moreover, the use of ethylene glycol as the lubricantduring theoperation of grinding the metal produces a powdered cop ch is moresuitable for the purpose of this-invention in that thephysical structureof each particle or granule of the copper is ofa more or less leafynature.

I Having prepared the copper in the -man-' her ust described it is addedto the solution of shellac and alcohol in the proportion of one tion.This mixture must be kept in a well stoppered bottle when not in use andmust be shaken well each time before usin The mirror, which may have asilver, gold or other type of reflecting surface, must be thoroughly drybefore the protective coating of .00 per is applied; thereto. When it isjudge thatthe reflecting surface of the mirror which is to be coatedwith copper is suf- .ficiently dry, the mixture of the ground cop perand its conveyor of shellac and alcohol is applied to the surface to becovered by a simple brushingfor spraying operation, a-

sufiicient quantity of this mixture being surface, it will be underpoundof copper to 24 ozs. of said solubrushed or sprayed over the metallicreflectingfih'n of the mirror to completely cover every portion of saidfilm. The chemical action of the copper which has been applied to themirror in the manner just described is such that in the'course of a dayor so afine ever, from the latter method in that while a film of purecopper is provided to cover the metallic reflecting film of the mirroran intermediate film of shellac is provided immediately over said latterfilm. The reflecting film is thus doubly protected, first b. a film orlayer of shellac and second by aiilm or layer of pure copper, the latterbeing in turn also covered by a film or layer of shellac.

The fact-that the protective layer of copr is separated from themetallic reflecting 1m of theimirror by the intervening layer of shellacprecludes the possibility of any chemical combine or reaction betweenthe reflecting film and its protective coatingwhich so frequently occurswhere the. latter is electrolytically deposited upon the former.

Also, due to the factthat the minute granules or particles of the groundcopper are of more or less leafy physical structure, when the aforesaidmixture is brushed or sprayed over the surface to be protected thesegranules or particles lay shingle-like uponfisaid surface to form auniform and regular protective film affording a maximum degree ofprotection. Each of these leafy p rticles being thoroughly coated withthe she lac dissolved in alcohol prevents actual metallic contact.between the reflecting surface of gold, silver or the like and theprotective film of copper in consequence of which spoilage of the mirroris reduced to a veritable minimum.

In place of ground and powdered copper, it will be understood that othermetals may be emloyed for the purpose of protecting the re ecting filmsof mirrors and reflectors from atmospheric and heat deterioration, theseother metals being similarly ground and powdered preparatory to mixingthe same with the solution oflshellac and alcohol. I have foundthataluminum, lead, tin and the like, either separately or in combination,when applied as protective coatings or backingsin the manner beforedescribed have the property of sealing the reflecting film against Y thedeleterious effects of moisture, gases and the like.

A combination of powdered metals which i for the'reflecting surfaces ofmirrors in 10- cations where the atmosphere. is extremelyv acid oralkaline is as follows p Parts 0 er if." 23 Lead 1 3 10 Antimony .5

' described of applying a protective coating For protecting thereflecting surface of mirrors and reflectors from intense heat, aluminum.has' been'found to be most satisfactory, the aluminum being ground andpowdered and then added to the aforesaid solution of shellac and alcoholin the proportion of one pound powder aluminum to 24 ounces of saidsolution, this mixture being readily applied to the surface to beprotected by a simple brushing or spraying operation.

It will be obvious that the method herein of metal to the reflectingsurfaces of mirrors and the like is extremely economical due to the factthat the necessity for expensive equipment and skilled labor is entirelyeliminated. In addition to this, tests have indicated that theprotective coatings of metal applied in accordance with the presentmethod are quite superior to those applied by any of the preserft knownmethods including the electrolytic deposition method wherein cop-.

per, when electrolytically deposited upon silver, combines and reactswith the silver to form ruinous blue streaks, particularly when thesilver reflecting film is thin and the atmosphere is such as to act asan electrolyte.

It will be understood, of course, that the invention is susceptible ofvarious changes from time to time without departing from the generalprinciples or real spirit of the claim the same broadly, as well asspecifically, as indicatedbv the appended claims.

What is claimed as new and useful is 1. A method of protectively coatingthe metallic reflecting film of a glass mirror or the like to protectthe same against spoilage due to exterior influences which consists inapplying to the rear surface of said mirror a free flowing mixture ofresinous material and comminuted copper particles of substantially leafyform.

2. A method of protectively coating the rear surface of a glass mirroror the like having a metallic reflecting film which consists indissolving by weight one part of shellac in about nine parts of alcohol,in adding powdered copper of leafy physical structure to said solutionin the proportion by weight'of about two parts of the metal to three of.the solution, and in applying the resultant mixture over the surface tobe protected.

3. In a glass mirror having a metallic reflecting film, a protectivecoating therefor consisting of comminutedcopper uniformly spread overthe rear surface of the mirror, each-particle of said copper beingsubstantially of leafy physical structure and covered with resinousmaterial, the latter serving not parts i sisting of minutely groundleafy particles of 7 inVention and it is accordingly intended to only asa binder for the comminuted copper but also as an insulating fihnbetween said copper and the metallic reflecting film.

4. In a mirror having a metallic reflecting film, a protective coveringfor said film con-

